Well, I got hit in the nuts by two different people now. They had a point to prove. And somewhere they both were right. But not everybody takes it the right way. I would first think about whether ur training partner will take it like a sport. If he doesn't it could lead to mean accidents. Someone who's hurt physically doesn't always see it as way of correcting, but as one of humiliation (negative, nothing to do with making somebody more humble, but trying to take away his worth). What if he doesn't show his anger through conversation, but decides to crank ur arm out of its socket during a pin? Just my 2 cents...